Electrooptical system



April 1936- J. R. HEFELE I ELECTROOPTICAL SYSTEM Filed May 51, 1955 juwQt I: u l:

INVENTOR y JR HEFELE B ATTORNEY Patented Apr. 14, 1936 UNITED STATESPATENT OFFICE Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application May 31, 1935, SerialNo. 24,219

7 Claims.

This invention relates to electrooptical systems and more particularlyto television.

An object of the present invention is to provide novel means forproducing an image of an object or field of view in natural color.

In order to produce a television image in natural colors, it isnecessary to combine light of the so-called, primary colors modulated inaccordance with the light-tone characteristics of the elemental areas ofthe object or field of view, an image of which is to be produced,several beams of modulated light to be simultaneously effective with thesynthesizing apparatus at the receiving station. It has already beenproposed to do this with a mirror helix as the synthesizing means bymixing the several beams of modulated light of primary colors in aso-called mixing box and using the mixed light with the helix as thoughit came from a single strip light source. This arrangement is relativelyexpensive and wasteful of light.

In accordance with this invention, the use of a mixing box is avoided,the light sources being used to supply light separately andsimultaneous- 1y to the helix. Each elemental area of the object orfield of view is scanned for each of the primary colors and theresulting plurality of. image signals for the same elemental area aregiven a phase difference with respect to each other just sufiicient tocompensate for the spacing of the light sources at the receiver andmakes unnecessary any optical mixing'means.

In the preferred embodiment of this invention, a scanning disc at thetransmitter has apertures and color filters therefor so arranged thateach elemental area of the object is scanned in close succession forred, green, and blue. The light reflected from the-object falls uponlight sensitive cells which respectivelyhave filters similar to thoseused with the apertures. Each of these filters passes a band of lightwaves having its center in the-appropriate color. The resulting imagecurrents are transmitted over separate communication channels toenergize strip light sources in each channel, respectively, whichpreferably are associated with appropriate filters to produce red,green, and blue light, respectively, as in a system using a mixing box.If the object at the transmitter is scanned at the same time for red,green, and blue, as is ordinarily done, the image seen by the observerin the mirror helix will consist of a red, a green, and a blue imageslightly displaced with respect to each other because of the physicaldisplacement of the red, green, and blue strip light sources from eachother. If, however, delay means, such as the delay introduced at thetransmitter by the scanning disc, are used, theimages produced by two ofthe sources are sufficiently delayed so that all three images are 5superimposed.

This invention is preferably adapted to reception of images televisedfrom a colored object or film, but is not necessarily limited to suchfor it could be used with a lenticular kodaco-lor film with the use ofappropriate light filters.

The invention will be more readily understood from the followingdescription taken in connection with the accompanying drawing forming apart thereof, in which:

Fig. 1 is a schematic diagram of a television system for producing animage of an object in color;

Fig. 2 shows a disc with three spirals of apertures used for scanningthe object; 20

Fig. 3 is an enlarged view of a portion of the scanning disc shown inFig. 2;

Fig. 4 shows the displacement of the red, green, and blue signals withrespect to each other; 25

Fig. 5 is a detail view showing the strip light sources used in thereceiving system; and

Fig. 6 shows a single element of the mirror helix used at the receiverin a situation where delay means at the transmitter are not used.

The invention will be hereinafter described as embodied in a televisionsystem employing three separate color bands, lying within the range towhich the eye is sensitive, and in which the predominant colors are,respectively, red, green, and blue. It should be clear, however, thatthe invention is not limited to the use of three channels nor to thesespecific colors.

Referring more particularly to the drawing, Fig. 1 shows a televisionsystem for the transmission of colored images. The system comprises atransmitter T, suitable connecting means (such as line or radio carrierchannels I, 2, and 3) and receiver R. Scanning apparatus at thetransmitting station T includes the powerful light source H), the lightfrom which is directed by a lens system H upon the scanning area of arotating disc l2, provided with a single spiral repeated three times asshown in Figs. 2 and 3. The path of the scanning light from the sourceI0 is through one of the apertures in the disc l2 and the aperture l3 ofa screen M, which latter aperture is so dimensioned that light comingthrough the aperture in the disc l2 can pass through a lens l5 and bedirected thereby to the object O, as in the ordinary beam scanningmethod.

The disc I 2, as shown in detail in Figs. 2 and 3 comprises a dischaving three apertures in place of each aperture of the usual singlespiral. This may be considered as three spirals. All of the apertures ofspiral l are covered with red filters, those in spiral 2 with greenones, and those in spiral 3 with blue filters. For each set of threeapertures (all apertures in a set have the same radius from the centerof the disc) an elementary line of the object is scanned for each of thethree colors, there being a slight delay between corresponding pictureelements for the difierent colors .due to the physical spacing of theapertures. The disc 12 is rotated by a motor I 6, at a substantiallyuniform speed, to completely scan the object once for each color perrevolution and within the period of persistence of vision.

The aperture I3 of the screen 14 is preferably so placed that the objectcan be scanned in a vertical direction so that a horizontal axis mirrorhelix can be used at the transmitter. In a situation where the objectscanned is a continuously moving film, the shape of the aperture l3would be similar to the one shown in Fig. 2 of a patent application ofH. E. Ives, Serial No. 700,413, filed December 1, 1933. Of course, it isto be understood that the object can be scanned horizontally as avertical axis mirror helix maybe used at the receiving station. In thislatter situation the aperture I3 would be at the top rather than at theside of the disc. Fig. 2 shows the placing of the aperture forhorizontal scanning while .Fig. 3 illustrates a position which issuitable 'for vertical scanning.

As the scanning disc I! rotates it causes moving beams .of intense lightof the primary colors respectively, to pass from the apertures n, 91,b1, etc. to scan the object O to be televised in a series of parallelpaths, eachelemental area being scanned in succession for each of .theprimary colors, and light representing the light-tone values ofsuccessively scanned elemental areas of the object is reflectedtherefrom and impressed upon a plurality of color selective, highlysensitive photoelectric cells I'l, l8, and J9, one for each color band.Each of the difierent photoelectric cells, as the result of the scanningoperation, is activated to cause the production of image currentsvarying in accordance with the color characteristics of the elementalareas of the object, and each is connected with an individualtransmission channel. The photoelectric cells I], I8, and H! are eitherinherently selective or made selective by positioning light filters 20,2|, and 22 between them and the object 0. By means of this colorselectivity, three electro-optical channels are established, and eachchannel is maintained from its origin at the light sensitive cell of thetransmiting station to its respective receiving lamp at, the receivingstation. A plurality of groups of color selective light sensitive cellsmay be used, in place of the single cells illustrated, and the cellsresponsive to the same color or spectral band are connected to the samechannels. The light cells of any group responsive to all of thedifferent colors are placed close together, so as to view the objectthrough as small an angle as is practicable in order to prevent thedifierent channels from producing their part of the received picture asthough the object were illuminated by differently located color lightsources, which would cause the produced image to show color fringes. Thedifier'e ent groups are preferably separated and diiTerently orientedwith respect to the subject so that the image will appear as though thesubject were illuminated from different positions.

The light energy, varying in accordance with the reflective power andthe color value of the elemental areas of the object being scanned, istranslated by the photoelectric cells El, E8, and [9 into electriccurrents. The currents from the color selective cells are amplified andcontrolled by suitable amplifiers 23, 24, and 25, one amplifier beinglocated in each channel. These amplifiers are arranged so that theamount of amplification for each channel can be adjusted, and thuspermit adjusting the output current in the channels. to the properstrength irrespective of any difference in response due to thesensitivity of the different light sensitive cells used for thediiferent spectral bands.

The incoming picture currents, transmitted over the different channels,are respectively impressed upon the amplifiers 26, 2?, and 25. Thecurrents transmitted over the channels are alternating currents ofvarying amplitudes representative of light variations above and belowthe average tone values of the successive elemental 1 areas of theobject being scanned and of their color characteristics. For anyparticular elemental area of the object O the picture signal channel Iwill be slightly ahead in time with respect to the signaling channel 2and similarly the signal in channel 2 will be slightly ahead of that inchannel 3.

Fig. 4 shows a typical image signal of an object which has a whiteelemental area (thus reflect ing all three primary colors) between twoblack elemental areas (reflecting none of the three coors). This figureshows plainly the efiect produce-d by the delay means in the signalcurrents as the increase in amplitude in the image current occurs laterin the green signal than it does in the red and still later in the blue.Of course, the order of scanning may be varied so as to be green, blue,red, or blue, green, red, instead of red, green, blue as abovedescribed.

The incoming image currents, after being amplified by the devices 26,21, and 28, are respectively applied to the strip light sources 29, 30,and 3|, arranged in the preferred embodiment with their axes horizontaland each adapted to supply light radiations of difierent wave-lengthscorresponding respectively to the wave bands respectively selected bythe devices [1, l8, and 19 of the transmitter. This may be effected byusing light sources which inherently produce light radiations of thedifferent wave-lengths or colors or by using sources for producing thedesired 'wavedengths and associating a light filter with each source,the respective filters being adapted to transmit radiations of thedesired wave-lengths while suppressing undesired wave-lengths.

Light sources 29, 30, and 3! may be of any suitable type adapted toproduce an elongated line of light which will vary in intensity with thevariations of the received image current. A more detailed view of theselight sources is shown in Fig. 5. Glow lamps, charged with inert gasesat a pressure of a few millimeters of mercury or lamps in which apositive column is produced in a capillary tube, may be used. When glowlamps are used, the gas charge may include a small percentage of activegas as disclosed and for the purpose set forth in an application of F.Gray, Serial No. 441,481, filed April 8, 1930. Thus, amplifier 26 maysupply image current from channel I to a neon lamp 29 having associatedtherewith, or not, as the case may be, a red filter 32; and

amplifiers 2'! and 28 may supply image current to argon lamps 3i! and3|, having associated therewith, respectively, a green filter 33 and ablue filter 34. For a more complete description of suitable lightsources and filters for the receiving station and filters for thetransmitting station, reference may be made to an article on Televisionin colors by a beam scanning method by H. E. Ives and A. L. Johnsrud inthe Journal of the Optical Society of America, January 1930, pages 11 to22.

The light sources 29, 30, and 3| are preferably placed in the sameplane, as shown in Fig. 5, in individual compartments of a lightproofreceptacle 35. The receptacle 35 has tiny apertures 36 (one for eachlight source) so that three parallel strip light sources are produced.

The light from these three sources is directed onto a mirror helix 3!preferably having a horizontal axis 38. This helix comprises a number ofrectangular strips threaded on the shaft 38 and progressively annularlydisplaced. This helix is constructed in accordance with the disclosurein a patent to H. E. Ives No. 1,964,580, issued June 26, 1934. Thereflecting faces of the mirror elements of the mirror helix 3'! arepreferably made concave cylindrical surfaces as described in thispatent. In this way, the light sources 29, 30, and 3| may be locatedcloser to the mirror helix 3'! for a given position of the observers eyeE than in the case where the reflecting surfaces are plane mirrors.

For the purpose of explaining the operation of this system, let it beassumed that the signals in the transmission channels I, 2, and 3 are inphase. The eye E of the observer would thus see a red, a green, and ablue image slightly displaced with respect to each other. If, however,means are introduced for delaying the signals in channels 2 and 3 withrespect to the corresponding signal in channel I, and if these signalsare delayed the proper amount, the image seen by the eye E in the mirrorhelix is a superposed image of the three light sources 29, 33, and 3|.As explained above, this desired delay is introduced at the transmitterby the use of the special scanning disc.

The method of operation of this system may be better understood byreferring to Fig. 6 where a single element of the mirror helix 3'! isshown. The mirror spiral is supposed to rotate in such a way on ahorizontal axis that the reflected images of the capillary lamps 29, 30,and 3| move upward in the direction of the arrow. If it is imagined thatthe red image is seen without delay at R, then the green and blue imageswould be seen at G and B, respectively, in the same phase as the imageat R. At some previous time, however, the red image has occupied thepositions G and B in turn, and if the spacing of the lamps 29,

33, and 3| is properly compensated for by the spacing of the aperturesof the scanning disc 12 the green and blue images can be put in thephase of the red image when it occupied these positions. The threeimages will then be identical and superposed. The actual delay in timedepends on the While there has been described a special scanning discfor introducing the delay in channels 2' and 3, it will, of course, beobvious to those skilled in the art that this invention is broad enoughto include any other means for introducing the delay in these circuitsfor the purpose desired in this system.

It is readily apparent that this invention does not require the use oflenses, mirrors, or prisms at the receiver for mixing the light from thecapillary lamps 29, 3B, and 3 I. The full intensity of the light fromthese normally low intensity gas discharge tubes is thus utilized and astronger and clearer image can be attained.

While this invention has been described for use in connection with amirror helix, it is obvious that any other suitable rotating scanningdevice having a plurality of light directing means each of whichsimultaneously cooperates with a plurality of fixed, separated lightsources for producing a composite image in color may be used as well,as, for example, a lensed disc,

Various other modifications may obviously be made without departing fromthe spirit of the invention, the scope of which is defined by theappended claims.

What is claimed is:

1. An electrooptical system comprising a re tating scanning devicehaving a plurality of light directing elements equal in number to thenumber of elemental lines of the image, a plurality of light sourcessimultaneously cooperating with each of said light directing elements inturn, said light sources being such that when light from the differentsources is mixed in different proportions, the various colors of thespectrum are produced, and means'for producing and impressing on saidsources, respectively, a plurality of independent out-of-phase imagecurrents respectively representative of the light-tone values of theelementa areas of the field of view taken in succession along parallelelemental strips thereof but for different primary colors corresponding,respectively, to the light from said sources, the difference ordifferences in phase of said currents being of such value as tocompensate for the separation of said sources, whereby a plurality ofcomplete images of said field are set up by said rotating scanningdevice in cooperation with said sources, which images are substantiallysuperimposed to produce a composite image in natural colors.

2. An electrooptical system for producing images in natural colorcomprising at a receiving station a mirror helix and a plurality ofstrip light sources such that when light from the different sources ismixed in different proportions, the various colors of the spectrum areproduced, said sources being parallel to the axis of rotation of saidmirror helix and having their long axes in different planes intersectingin said axis, and means for producing and impressing on said sources,respectively, a plurality of independent out-of-phase image currentsrespectively representative of the light-tone values of the elementalareas of the field of view taken in succession along parallel elementalstrips thereof but for different primary colors corresponding,respectively, to the light from said sources, the difference ordifferences in phase of said currents being of such value as tocompensate for the separation of said sources, whereby a plurality ofcomplete images of said field are set up by said helix in cooperationwith said sources, which images are substantially superimposed toproduce a composite image in natural colors.

3. An electrooptical system comprising a rotating scanning device havinga plurality of light directing elements equal in number to the number ofelemental lines of the image, a plurality of light sourcessimultaneously cooperating with each of said light directing elements inturn, said light sources being such that when light from the differentsources is mixed in difierent proportions, the various colors of thespectrum are produced, means at the transmitter for producing aplurality of independent out-of-phase image currents respectivelyrepresentative of the light-tone values of the elemental areas of thefield of view taken in succession along parallel elemental stripsthereof but for different primary colors corresponding, respectively, tothe light from said sources, and means for impressing these out-ofphaseimage currents on said sources, the differ-' ence or differences inphase of said currents being of such Value as to compensate for theseparation of said sources, whereby a plurality of complete images ofsaid field are set up by said rotating scanning device in cooperationwith said sources, which images are substantially superimposed toproduce a composite image in natural colors.

4. An electrooptical system comprising a 1'0- tating scanning devicehaving a plurality of light directing elements equal in number to thenumber of elemental lines of the image, 'a plurality of light sourcessimultaneously cooperating with each of said light directing elements inturn, said light sources being such that when light from the differentsources is mixed in different proportions, the various colors of thespectrum are produced, means at the transmitter for producing aplurality of independent out-of-phase image currents respectivelyrepresentative of the light-tone values of the elemental areas of thefield of view taken in succession along parallel elemental stripsthereof but for difierent primary colors corresponding, respectively, tothe light from said sources, means for impressing the respective out-Of-phase image currents upon different transmission channels fortransmission to a receiving station including said light sources, thedifference or differences in phase of said currents being of such valueas to compensate for the separation of said sources, whereby a pluralityof complete images of said field are set up by said rotating scanningdevice in cooperation with said sources, which images are substantiallysuperimposed to produce a composite image in natural colors.

5. An electrooptical system as described in claim 1 in which a scanningdisc is used to introduce the difference or differences in phase of thecurrents corresponding respectively to the different primary colors.

6. An electrooptical system as described in claim 1 in which a scanningdisc is used to introduce the difference or differences in phase of sthe currents corresponding respectively to the different primary colors,said scanning disc comprising anumber of spirals of apertures, thenumber of spirals corresponding to the number of primary colors used,and the spirals being respectively displaced from each other by adistance less than the length of a scanning line.

7, An electrooptical system for producing images in natural colorcomprising at a receiving station a mirror helix and a plurality ofstrip light sources such that when light from the different sources ismixed in different proportions, the Various colors of the spectrum areproduced, said sources being parallel to the axis of rotation of saidmirror helix and having their long axes in different planes intersectingin said axis, and means at a transmitting station for setting up imagecurrents for said receiving station comprising means for scanning inelemental parallel strips in succession a field of view and eachelemental area of each strip for each of a plurality of primary colorscorresponding to the colors of said sources at the receiving station,said scannings of the same elemental area being separated in time by anamount less than a strip scanning period and just sufficient tocompensate for the effect of having said sources at the receivingstation spaced apart, whereby a plurality of complete images of saidfield are produced in said primary colors, respectively, and aresubstantially superimposed to produce a composite image in naturalcolors.

JOHN R. HEFELE.

